Ever since Thomas Edison invented the phonograph in the 19th Century, audiophiles have made continuing efforts to improve the quality of mass reproduction of sound. Some of these attempts have gone off in widely varying directions, such as those represented by magnetic tape and digital optical disks. However, by far the most popular method of mass reproduction of music and other sound phenomena is by the use of vinyl disks known as "records". These records are recorded with physical perturbations within a spiral groove which correspond to the sounds recorded. The completed record, be it an album or single, is then placed on a phonograph connected to electrical or electronic signal translating equipment which then, to a greater or lesser degree, reproduces the original sounds.
The phonograph has several key elements. One of these is the pickup element which actually engages the record disk and receives the vibrations from the perturbations within the grooves. The pickup element is ordinarily carried on a tone-arm of any of several designs while the record disk itself is caused to rotate with respect to the pick-up element by a turntable or a similar element. The present invention deals with the pickup element portion of the phonograph which translates the perturbations into electrical signals.
On an older or less sophisticated phonograph record playing apparatus, the pickup element may be a simple needle or rigidly mounted stylus, without any particular integrated vibrational translation apparatus. However, modern equipment, at least on the higher quality levels, utilizes elements known as "phonocartridges" which include a stylus, which actually engages the record groove, and various other elements which translate the vibrations in the stylus to electrical signals which are then delivered along the tone arm wiring to the electrical equipment which translates the signals back into sound waves which theoretically match those originally recorded. Phonocartridges have advanced from mere preamplifiers of the signals to highly sophisticated vibrational translating elements as technology has improved.
One type of phonocartridge which has achieved great popularity is that known as a moving coil phonocartridge. A prime example of a previously known method of achieving moving coil signals based on a stylus and cantilever is shown in FIGS. 1 and 2 of U.S. Pat. No. 3,679,843, issued to Cho on Jan. 4, 1971. The operational characteristics of the prior art cartridges utilize a magnet and a series of non-permanently magnetic, but magnetically conducting, yokes to shape the field about windings which are carried within the magnetic field and are caused to vibrate therein by the tracking of a stylus on a record groove. This type of audio pickup mechanism, and various improvements thereon, have become a standard type of phonocartirdge within the industry.
Some of the improved versions of the basic moving coil type phonographic pickup cartridge are, in addition to Cho, U.S. Pat. No. 3,956,598, issued to Kawakami, et al on May 11, 1976, U.S. Pat. No. 3,299,219 issued to Madsen on Jan. 17, 1967 and U.S. Pat. No. 3,963,880 issued to Ikeda on June 15, 1976. Some precursors of this technology are found in U.S. Pat. No. 3,236,955, issued to Klemp, at al on Feb. 22, 1966 and U.S. Pat. No. 3,040,136, issued to Grado on June 19, 1962.
Numerous commercially available phonocartridges also use the prior art technology. One such series of cartridges, known as the Talisman family, manufactured by Sumiko, Inc. of Berkeley, Calif., exemplifies this technology. This family, which includes the Talisman S, Talisman B and Talisman A cartridges represents an improved version of the basic technology in that it eliminates intermediate yokes and utilizes only a single magnet with a front pole piece. The front pole piece, which is not a permanent magnet but is magnetically conductive, acts to shape and intensify the magnetic field created by the rear magnet.
Although the prior art cartridges have been capable of extremely good sound reproduction and high quality output, there always remains room for improvement. It is always desirable to create a cartridge with an extremely low stylus tip mass. It is also desirable to construct cartridges which have the fastest possible rise time and capability of responding to the widest possible range of frequencies (widest band width).
It is also desirable to eliminate stray signals and unintentional perturbations of the magnetic field. These can be caused by eddy currents which may occur in pole pieces and yokes. It is also preferrable to eliminate magnetic fringe fields whenever possible.
The technology of pressing records in modern time has achieved such great precision that auditory differences may be heard when cartridges of less than perfect design are utilized, as compared with the ultimate possibilities. Therefore, the industry continues to attempt to achieve phonocartridges having the maximal response characteristics at low weight and at as low of a cost as possible.